The Attraction of Trypanosoma cruzi to Vertebrate Cells In Vitro

SYNOPSIS. A video technic is described that permits a quantification of the degree of attraction of Trypanosoma cruzi trypomastigotes to vertebrate cells in vitro. Bovine embryo skeletal muscle cells (BESM), HeLa cells and Vero cells all attract a myotropic strain of T. cruzi trypomastigotes. BESM cells, however, are 2-fold more attractive to trypomastigotes than HeLa cells and 10-fold more attractive than Vero cells. Heat-inactivation of BESM cells abolishes their ability to respire and also to attract T. cruzi trypomastigotes. As there is no difference in the endogenous oxygen consumption between BESM, HeLa, and Vero cells, it is unlikely that differences in the attraction of trypomastigotes to the 3 cell types are due to variations in the magnitude of pO₂ or pCO₂ gradients in the milieu around the cells.     

Development of powdery mildew on leaves of several barley varieties at different growth stages

On detached leaves and intact plants of several barley varieties at different growth stages, lower percentages of germinated conidia of Erysiphe graminis f.sp. hordei penetrated the host and initiated infection on the abaxial than adaxial surface. More and larger E. graminis colonies developed on the adaxial surface and these comprised more densely packed hyphae and produced more conidiophores than did colonies on the abaxial surface. These results are consistent with the observation that there is usually more powdery mildew on the adaxial than abaxial surface of barley leaves in the field. Smaller proportions of germinated E. graminis conidia penetrated and infected the host on leaves of adult or near-adult plants than on those of seedlings or juvenile plants. Older plants also supported fewer, smaller and less dense colonies with less sporulation than young plants. The effects of growth stage of the host plant on development of powdery mildew were much greater in some barley varieties, and with some E. graminis isolates, than others.     

Cell Division Heterogeneity in the Primary Meristems of Pisum sativum Root Tips after Excision

Root tips (1.0 cm) were excised, transferred to culture medium,sampled at intervals, embedded in paraffin and sectioned. Themitotic index in each primary meristem in the 2.0 mm tips wasreduced immediately after excision. After 8–12 h mitosisresumed. The position of mitotic figures in the protoderm, groundmeristem, procambium, and root cap was determined. The greatestnumber of mitotic figures occurred in the procambium, and uponexcision the smallest percent reduction also occurred in thisregion. The ground meristem showed the greatest reduction inmitotic figures. After excision, the relative contribution tothe total number of mitotic figures increased in the procambiumtissue and decreased in the ground meristem. Cell division inall primary meristems of the root tip is reduced after tip excision,but the ground meristem (cortical region) is the primary targettissue.     

Chemistry of sediments from two linked lakes in North Wales

SUMMARY. Cores of sediment from Llyn Peris and Llyn Padarn, two linked lakes in North Wales, are described. Dating of sediments by ¹⁴C techniques, investigations of remanent geomagnetism and estimates of recent deposition rates from measurements of ¹³⁷Cs, indicate that in Padarn an unbroken record of the last 7000 years has been obtained. In Peris, the upper lake, the rate of sediment accumulation is greater than in Padarn and the sediment has been considerably disturbed. Sediment chemistry is related to the climatic and industrial history of the area. Some features of the chemical profiles in Padarn are similar to those of lakes in the English Lake District, and there is evidence to suggest that erosion has increased in the catchment since c . 3500 years ago. This is more recent than similar increases in erosion reported for the English Lake District. In Peris, industrial activity during the past few hundred years has resulted in high levels of copper and calcium in the surface regions of sediment profiles.